The present invention relates to an exhaust gas turbocharger for an internal combustion engine and a corresponding method.
German Published Patent Application No. 42 13 047 describes an exhaust gas turbocharger for an internal combustion engine, the compressor of which is driven by the turbine of the charger and compresses combustion air from atmospheric pressure to a higher charge pressure during the operation of the internal combustion engine. In order to improve the transient characteristics of the exhaust gas turbocharger, compressed air can be supplied to the compressor via an additional channel, which supports in particular the increase in charger speed from low to higher peripheral speeds. This mode of operation is used in low-load ranges, where there is only a relatively small exhaust gas counterpressure which can be used to drive the charger.
The compression characteristics can be manipulated at selected operating points by supplying compressed air, which may partially compensate for a slower charge pressure buildup. This advantage, however, is obtained at the expense of a higher design and control complexity. In particular, a compressed air generating unit and a compressed air storage device, including the supply lines to the compressor and various actuating and shutoff devices are required.
It is an object of the present invention to expand the range of utilization of exhaust gas turbochargers using simple arrangements and to improve their operating characteristics.
The above and other beneficial objects of the present invention are achieved by providing an exhaust gas turbocharger and method as described herein.
The exhaust gas turbocharger according to the present invention for an internal combustion engine includes a compressor with a compressor inlet channel, in which an adjustable shutoff element is arranged upstream from the compressor rotor for the variable adjustment of the effective cross-section of the compressor inlet channel. This arrangement provides the advantage that the cross-section of the compressor inlet channel may be variably adjusted, allowing the operating characteristics of the compressor to be manipulated in a targeted manner. In particular, the flow velocity and the swirl of the supplied combustion air may be manipulated. The flow inlet velocity of the supplied air may be increased, for example, by narrowing the effective cross-section. The swirl with which the combustion air impinges on the compressor rotor may also be modified by narrowing or widening the effective cross-section.
At certain operating points of the internal combustion engine, in particular at low loads or low setpoint charge pressures, the compressor may also be used as an air-driven turbine via the manipulation of the flow inlet velocity and the swirl by reducing or widening the effective cross-section in the compressor inlet channel, e.g., without reversing the direction of rotation of the compressor rotor. In a turbine operating mode of the compressor, the charge pressure to be supplied to the internal combustion engine downstream from the compressor is lower than the atmospheric pressure. Thus, there is a pressure gradient across the compressor in the direction of flow. In the low-load range too, a pressure drop across the compressor, for which the pressure at the compressor inlet is higher than at the compressor outlet, i.e., the engine cylinder inlet, may also be created. This pressure gradient across the compressor corresponds to throttling in the intake system. It generates a vacuum in the intake manifold and makes it possible to operate the internal combustion engine without a throttling valve in the intake manifold even in the low-load range. Thus, the internal combustion engine may be basically operated over the entire operating range without a throttle valve, and the intake pressure may be regulated via the compressor exclusively.
The compressor may include both a semi-axial and a radial flow inlet cross-section to the compressor rotor, it being possible to manipulate the semi-axial flow inlet cross-section via the shutoff element for variable cross-section adjustment. However, it may also be possible, if necessary, to provide an adjustable shutoff element in the radial flow inlet cross-section as an alternative or in addition to a shutoff element in the semi-axial flow inlet cross-section.
The semi-axial flow inlet cross-section may be variably adjusted between a closed position and an open position via the shutoff element, with full shutoff of this cross-section being set in the closed position, so that the entire air mass flow is supplied to the compressor rotor via the radial flow inlet cross-section. A guide grid, through which the swirl with which the supplied air impinges on the compressor rotor may be influenced, may be arranged in the radial flow inlet cross-section. This guide grid has a variable design, allowing the radial flow inlet cross-section to be variably adjusted during the operation of the internal combustion engine.
A partition, which is may be arranged in the form of a ring in the compressor inlet channel and delimits an outer annular channel through which combustion air may be supplied to the radial flow inlet cross-section, may be provided between the semi-axial and radial flow inlet cross-sections. This annular channel, arranged coaxially to the compressor rotor, allows combustion air to recirculate in certain operating ranges of the compressor in order to shift the pumping limit of the compressor toward an extended operating range of the compressor. During recirculation, a partial mass flow is supplied back into the inlet area of the compressor through the annular channel and re-aspirated together with the main flow. Thus, the pumping capacity of the compressor may be increased.
The compressor inlet channel, which may include an air filter, may be configured as an annular collection chamber, in the center of which the shutoff element is arranged, which may be annularly surrounded by the compressor inlet channel. The compressor inlet channel communicates with a compressor rotor chamber, which accommodates the compressor rotor, via a flow inlet cross-section, it being possible to adjust the effective flow inlet cross-section in the inlet area of the compressor rotor, for example, via an exclusively axial displacement of the shutoff element in the axial direction of the charger.
In the method according to the present invention, the effective cross-section in the compressor inlet channel may be variably adjusted during the operation of the internal combustion engine. This method may be combined, for example, with one or more of the previously described features.